Black Holes: The Weird Science of the Most Mysterious Objects in the Universe
DATA FROM FOUR DIFFERENT TYPES OF TELESCOPES CREATED THIS IMAGE OF THE SPIRAL GALAXY MESSIER 106 ALSO KNOWN AS NGC 4258 AT THE CENTER OF THIS GALAXY IS A MASSIVE BLACK HOLE 1 WHAT IS A BLACK HOLE F irst things first Did you know that black holes are made of warped space and warped time They have mass but no matter Their gravitational pull is so great that nothing not even light can escape their grasp They sound simple until you try to wrap your brain around them Even Albert Einstein a physicist whose general theory of relativity 1915 predicted the existence of black holes refused to believe that they were real In a 1939 paper Einstein said The essential result of this investigation is a clear understanding as to why the Schwarzschild singularities as black holes were known at the time do not exist in physical reality Or nice idea pal but hey we live in the real world To really understand black holes and maybe to feel smarter than Einstein when you realize they really do exist it helps to take a trip back in time 5
All the way back in fact to the late seventeenth century That’s when an apple falling from a tree is said to have led English physicist and mathematician Sir Isaac Newton to formulate his law of universal gravitation GRAVITY IT’S NOT JUST A GOOD IDEA IT’S THE LAW By the mid-sixteenth century scientists had discovered that the planets in our universe travel around the sun in an elliptical oval pattern Nobody knew why the planets moved that way or what kept them in orbit Newton OH THAT’S JUST A THEORY In everyday conversation people tend to use the word theory to describe a hunch or guess Evolution say creationists people who believe in the biblical explanation for the creation of the universe That’s just a theory In fact evolution is a theory To scientists a theory is not a half-baked idea A theory explains a collection of facts about some aspect of the natural world It can be tested and used to make predictions Peter Godfrey-Smith a philosopher of science at the City University of New York and at the University of Sydney in Australia compares theories to maps Just as a map represents an area of land a theory represents a territory of science A road map shows highways rivers and cities that we know exist In the same way a theory is made up of observable facts A good theory like a good map is an accurate depiction of the physical world It’s important to understand the difference between facts laws hypotheses and theories When an apple drops from a tree it falls down not up That’s a fact Newton’s law of universal gravitation describes the observation that the apple falls down
tackled that problem in his 1687 book Philosophiæ Naturalis Principia Mathematica Mathematical Principals of Natural Philosophy known as the Principia for short In it he described three laws of motion Although it took Newton more than five hundred pages to explain his laws they boil down to three sentences Every object stays in its state of rest or uniform motion in a straight line unless some kind of force acts upon it It allows us to calculate all sorts of things about a falling apple the strength of the gravitational pull between it and Earth its acceleration as it falls how long it will take to hit a daydreaming Newton on the head and so on THE HOW AND WHY OF GRAVITY What Newton’s law doesn’t tell us is why gravity exists or how it works Scientists develop testable hypotheses or smart guesses to explain observations Until the late nineteenth century scientists believed that gravity was due to what scientists call ether tiny invisible particles all around us that pushed things down But the evidence didn’t support that hypothesis so scientists rejected it Einstein proposed that what we perceive as gravity is actually the result of a distortion in the fabric of space and time Einstein’s hypothesis held up through repeated observation and experimentation So it became a scientific theory the general theory of relativity Not only did Einstein’s theory explain gravitational attraction but it also predicted gravitational waves and black holes Theories may change as scientists make new discoveries They can be adapted to include that new knowledge 7
